Method for heat development



United States Patent 3,257,205 METHOD FOR HEAT DEVELOPMENT Paul Maria Cassiers, Mortsel-Antwerp, Louis Maria De Claims. c1. 96- 29) This invention relates to an improved method for the manufacture of photographic images by a dry processing of photographic silver halide emulsions and to material for the application of this method.

It is known from the German patent specification 888,- 045 that photographic layers can be obtained which are developable by heat,-by incorporating into silver halide emulsions substances which reduce silver halide salts, such as hydrazine, phenyl hydrazine, acid hydrazides, semiice good results when used in this new method, are identified hereinafter:

1-phenyl-3-pyrazolidone l-(m-tolyl) -3-pyrazolidone 1 phenyl-2-acetyl-3-pyrazolidone 1-phenyl-4 methyl-3-pyrazolidone l-phenyl-5-methyl-3-pyrazolidone 1-phenyl-4,4-dimethyl-B-pyrazolidone 1-phenyl-5,5-dimethyl-3-pyrazolidone 1,5 -diphenyl-3-pyrazolidone l-(rn-tolyl) -5-phenyl-3-pyrazolidone 1-(ptolyl)-5-phenyl-3-pyrazolidone carbazides, methyl-p-aminophenol sulphate, hydroquinone and pyrocatechol.

Other suitable reducing compounds for heat development processes are aromatic amino-, hydroxy-, and aminohydroxy-compounds and their derivatives, many examples of which are described in German patent specification 895,101 and Belgian patent specifications 544,850,

545,042 and 555,103.

The use of the developing substances, however, which are described in these patent specifications, involved various disadvantages. Especially the keeping quality of such emulsions before exposure leaves much to be desired.

Also the image obtained is of an inferior quality because of the too low density and the too soft gradation of the light-sensitive material.

According to the present invention a process has been found for the production of photographic images by heatdevelopment, wherein a photographic material comprising a silver halide emulsion layer and incorporated in this silver halide emulsion layer and/or in a layer adjacent thereto, a S-pyrazolidone compound of the formula wherein:

after or during exposureto an object to be reproduced, is subjected to a heat treatment, the pH of the silver halide emulsion during the heat-development being 7 or less.

Some compounds according to the present invention, which appeared from the experiments to give particularly 5-phenyl-3-pyr-azolidone The developing substances according to this invention may be incorporated, either into the silver halide emulsion or into a separate adjacent layer.

The best known of these developing substances viz. l-p-henyl-B-pyrazolidone on itself possesses only poor developing properties as far as development in aqueous medium is concerned (J. D. Kendall, Brit. J. Phot. (1951) 539). It is really surprising that these substances, even when used in the absence of any other developing substance, possess a high developing power if used in a pho-v tographic material subjected to heat-development. Still more unexpected is the fact that this strong developing power even occurs not only in neutral and weak acid medium, but even in relatively strong acid medium, e.g., of pH 4.5.

The developability of the above described silver halide emulsions can still be improved by incorporating into these emulsions compounds which on heating liberate water.

The use of hydrophilic plasticizers, e.g., glycerol, caprolactam, polyethylene glycol and the like, also results into an improvement of the heat-developa-bility. Also in this kind of emulsions the image quality can be improved by incorporating into the emulsions compounds which favorably influence the image tone, e.g., l-phenyl-S-mercaptotet-razole or similar products, which are described in British patent specification 561,875 and Belgian patent specification 502,525.

An advantage of the new process is the excellent quality of the produced images with regard to the density as well V as in respect of the gradation. After rinsing and fixing, the obtained density is also much better kept than it is in the case with the most known developing substances.

A second advantage is the short developing time: in some cases the development has to last for only 1 to 10 sec. at a temperature between and 200 C. Furthermore, the material according to the invention has very good keeping properties'before its exposure, as derivatives of 1-phenyl-3-pyrazolidone in a non-alkaline medium and a normal temperature show but a poor reactivity.

A further advantage is the broad thermal margin of working up or the silver halide emulsions which are prepared with these new compounds. It has been experienced that the temperature fluctuations during the heatdevelopment may amount to 30 to 40 C. without incurring the risk that less good images are obtained.

The amount of warmth which is necessary for the development may be applied onto the material in various waves possess a wave-length of to 10" cm.

ways. So the silver halide emulsion can be developed by conduction, by contacting it with heated plates or rollers, by placing it between two capacitor plates which are subjected to a high frequency field, or by subjecting it to the Joule effect. The silver halide emulsion can also be developed by convection, e.g., by contacting it with directed warm gas stream. For this purpose, e.g., warm air or steam may be used. Finally the silver halide emulsion can also be developed by warmth radiation. The use of infrared radiation sources is especially suited therefor, not only because they have an intensive developing power, but also because they enable simultaneously to expose and to develop in a fraction of a second. By infrared radiation sources those radiation sources are understood of which the major part of the radiated energy In this way it is possible to contact a light-sensitive material, prepared according to this invention, with a film negative and to move it along a light-source which is rich in infrared radiations so as to obtain immediately a very strong positive image.

An especially interesting embodiment of this invention is the manufacture of prints of the heat-developed images according to the transfer process, which is described in the German patent specification 895,101. As is described in that German patent specification the silver halide layers which are developable by heat, contain a developing sub- 4, (1,2)triazolium chloride and 2-phenyl-3-(o-carboxyphenyl) -naphtho 1,2) triazolium chloride.

Some tetrazolium compounds according to the above Formula III which appeared from the experiments to give particularly good results are, e.g., 2,5-diphenyl-3-(o-carboxyphenyl)-2,l,3,4-tetrazoliurn chloride, 2,5-diphenyl-3- (o-methoxyphenyl)-2,l,3,4-tetrazolium chloride and 2,5- diphenyl 3 (p-methoxyphenyU-Z,1,3,4-tetrazolium chloride.

stance which, by reduction of the silver halide to silver on the exposed image areas, is used up and which on the unexposed image areas diffuses under the influence of the supplied warmth into an image-receiving layer brought into contact with the silver halide emulsion layer.

Analogously the process according to the present invention can be carried out by contacting the negative layer containing the developing substance, before the heatdevelopment, with a positive layer containing a colorless triazolium compound of the general formula wherein:

each of R and R (equal or different) represents an aliphatic group, a substituted aliphatic group, a homocyclic group, a substituted homocyclic group, a heterocyclic group, or a substituted heterocyclic group;

X represents an acid radical, and

Y represents the necessary atoms for closing an homocyclic group, substituted homocyclic group, a heterocyclic group, or a substituted heterocyclic group.

Such triazolium compounds are described, e.g., in French patent specification 998,055.

According to another embodiment of the present invention, the negative layer is contacted, before the heatdevelopment, with a positive layer which contains a colorless tetrazolium compound of the formula:

The development substances which remained unused during the heat-development, diffuse into the positive layer and there reduce the above .mentioned colorless triazolium and tetrazolium compounds to dyes. The color tone, the fastness to light and the fastness to washing of these dyes can markedly be improved by the presence in the positive material of salts of multivalent metals, e.g., zinc, copper,

iron, cadmium, cobalt, nickel, chromium, titanium, molybdenum, or tungsten, if tetrazolium compounds are used wherein R is an aryl radical, which in its ortho position bears an electronegative group such as a canboxyl group.

Another interesting embodiment of this invention is based on the formation of a silver image in the positive material. For this purpose, the exposed negative is contacted during the heat-development with a positive material containing silver salts, e.g., silver nitrate. The developing substances which remain unused during the heatdeveloprnent diffuse into the positive layer and there reduce the silver salts into metallic silver.

The following examples illustrate the invention without limiting, however, the scope thereof. The silver halide emulsion layers in the dried light-sensitive materials preferably contain per sq. m. 3 g. of gelatin and an amount of silver halide corresponding to 1 g. of silver.

Example 1 A photographic paper support of 90 g./ sq. m. is coated with a layer from a suspension of the following composi- This paper is then dried, exposed through an original and heat-developed either by contacting this paper with a plate heated at 200 C. or by treating it with a steam jet of 100 C. A sharp print of the original is obtained. This print may be fixed and stabilized according to known processes.

Example 2 A photographic paper support of -g./sq. m. is coated with a layer from a suspension of the following composition:

Silver bromide emulsion g 1000 Water ..cm... 465 Ethanol crus ...v 400 1-phenyl-3-pyrazolidone g 25 Caprolactam g Saponine g 5 40% aqueous formaldehyde solution cm. 5

After further treatment, exposure and heat-development as in Example 1, a sharp print of the original is obtained.

Example 3 A photographic paper support of 90 g./sq. m. is coated with a layer from a suspension of the following composition:

Silver chloride emulsion 'g 1000 Water cm. 465 Ethanol cm. 400

5 p Carbowax 200 (trade name of Union Carbide and Carbon, New York, N.Y., for a polyethylene After further treatment, exposure and heat-development as in Example 1, a sharp print of the original is obtained.

Example 4 A negative material is prepared by coating a paper support of 90 g./sq. m. with a layer from a suspension of This layer is applied in such a way that 1 l. of this suspension covers 10 sq. m. of paper. Upon this layer is then applied a layer from the following solution:

Ethanol cm. 1000 l-phenyl-3-pyrazolidone g 50 This layer is applied in such a manner that 1 l. of this solution covers 20 sq. m. of paper.

A positive material is prepared by dip-coating a paper support of 90 g./sq. m. with a 0.1% aqueous silver nitrate solution and drying it.

The silver halide emulsion side of the negative material, 'in contact with the original, is reflectographically exposed. The negative material is pressed for about 5 sec. with its emulsion side against the prepared positive material by means of a flat-iron at about 150 C.

The part of developing substance which during the heat-development did not serve to reduce the silver halide into silver, diffuses onto the positive layer and reduces the silver nitrate into silver. A clear print of the original is obtained.

Example 5 A photographic paper support of 90 g./ sq. m. is coated with a layer from a suspension of the following composition:

Silver chloride emulsion cm. 100 Water cm. l Ethanol cm. 1-phenyl-3-pyrazolidone g 1 Potassium metabisulfite g 1 Sodium acetate g 20 99% acetic acid cm. 3 Saponine cm. 0.5 40% aqueous formaldehyde solution cm. 0.5 1% solution of l-phenyl-S-mercapto-l,2,3,4-tetrazole in ethanol cm. 2.5 Titanium dioxide g 6 This layer is applied in such a way, that 1 l. of this suspension covers 10 sq. m. of paper.

A positive material is prepared by coating a paper support of 90 g./sq. m. with a layer from a solution of the following composition:

5% aqueous solution of gelatin cm. 50 l aqueous solution of 2,5-diphenyl-3-(p-methoxyphenyl)-2,1,3,4-tetrazolium chloride CIIL3 10% aqueous solution of cupric sulfate cm. 5 20 g. of anhydrous sodium acetate dissolved in water to cm. 24 10% aqueous formaldehyde solution cm. 0.5

The negative material is refiectographically exposed to a printed original and developed by pressing it for 10 sec. against a heated plate at 110 C. Then the developed the following composition:

Silver chloride emulsion g 1000 .Water cm. 1000 Glycerol cm. 100 Saponine g 5 aqueous formaldehyde solution cm. 2

negative material is contacted with the positive material for 20 sec. at C. After separation of the materials, a strong red print of the original is obtained onto the positive material.

Examples 6-7 Similar results are obtained by replacing in the above solution the 2,5 diphenyl-3-(p methoxyphenyl)-2,l,3,4- tetrazolium chloride by a same amount of 2,5-diphenyl-3- (o-methoxyphenyl)-2,l,3,4-tetrazolium chloride or 2,3-diphenylnaphtho (1,2)triazolium chloride.

We claim:

1. A process for the production of photographic copies by heat development which comprises the steps of:

(1) Exposing to the object to be copied a photographic material comprising a silver halide emulsion layer and containing a compound liberating moisture on heating and a 3-pyrazolidone developing compound of the general formula:

R5 N R5 G/ \NR2 R4C-CO wherein:

R is a member of the group consisting of hydrogen and an aryl radical, R is a member of the group consisting of hydrogen and an acyl radical, and R R R and R are each a member of the group consisting of hydrogen, an alkyl radical and an aryl radical;

(2) Developing said exposed emulsion layer by subjecting said layer to a heat treatment at a pH of not more than 7 while said material is maintained in effective separable contact with an image-receiving layer containing an initially colorless image-forming compound selected from the group consisting of (1) silver nitrate, (2) a triazolium compound having the general formula:

wherein:

R and R are each a member of the group consisting of an aliphatic group, a homocyclic group, and a heterocyclic group,

X is an acid radical, and

Y represents the atoms necessary for closing a ring of the group consisting of a homocyclic ring and a heterocyclic ring;

and (3) a tetrazolium compound having the general formula:

N l T (References on following page) UNITED STATES PATENTS 554 934 3/32; geigium. e glum. et 998,055 1/1952 France. James 9629 5 1,003,578 9/1952 Germany. Allan 96109 670,883 4/1952 Great Britain. Hydn et a1. 9629 845,928 8/1960 Great Britain. Hydn et a1. Herrick et aL d 96*29 NORMAN G. TORCHIN, Przmary Examiner. Haist et a1. 96-95 10 LOUISE 'P. QUAST, Examiner. Roth 9629 FOREIGN PATENTS J. T. BROWN, Assistant Examiner. 

1. A PROCESS FOR THE PRODUCTION OF PHOTOGRAPHIC COPIES BY HEAT DEVELOPMENT WHICH COMPRISES THE STEPS OF: (1) EXPOSING TO THE OBJECT TO BE COPIED A PHOTOGRAPHIC MATERIAL COMPRISING A SILVER HALIDE EMULSION LAYER AND CONTAINING A COMPOUND LIBERATING MOISTURE ON HEATING AND A 3-PYRAZOLIDONE DEVELOPING COMPOUND OF THE GENERAL FORMULA: 